The present invention relates to an optical device for use in, e.g., an optical printer, copier or scanner and a method of fabricating an aperture array for shielding light.
An array type optical device including an input aperture array and an output aperture array is conventional. The input aperture array has a plurality of input apertures formed at a preselected period of arrangement. The output aperture array has a plurality of output apertures formed at a preselected period of arrangement and respectively facing the input apertures. Light incident to the optical device via a desired one of the input apertures is output via the output aperture aligned with the desired input aperture. This type of optical device is included in, e.g., an optical printer, facsimile apparatus, copier or scanner in order to write a latent image electrostatically or to focus an image read. The prerequisite with such an optical device is that light expected to be output via a particular output aperture is prevented from reaching the other output apertures as stray light.
Japanese Patent Publication No. 63-11647, for example, teaches a lens array in which an image input to a single thick lens from an object plane is inverted in the lens and then output via an output plane to be focused in a 1:1 magnification. In this lens array, an absorption layer is provided on the side of each lens other than a curved surface in order to prevent light from leaking to the adjoining lenses. So long as the lens itself is large size, the side of the lens can be easily shielded from light. However, for a compact configuration, it is necessary to reduce the focal distance of the lens and therefore to reduce the diameter of the lens to less than 1 mm. For this reason, mirror tubes serving to shield light at the same time are arranged to constitute a lens array, as described in the above document. In this case, arranging small tubes side by side is not practical because not only the number of parts but also the size of the assembly increase. The tubes are therefore replaced with tubular shield films. However, a lens array with such tubular shield films is difficult to fabricate because the ratio of the length of the tubes to the diameter of the same (aspect ratio) increases with a decrease in the size of the lens array.
Japanese Patent Laid-Open Publication No. 8-1998 discloses an optical device implemented as a print head having an LED (Light Emitting Diode) array chip and a protection layer (shield layer) covering the light emitting surfaces of LEDs. The protection layer is formed with through holes for passing light emitted from the individual light emitting surfaces. Assuming that the LEDs are arranged at a pitch of 600 dpi (dots per inch), then the through holes are arranged at a period of 42.5 .mu.m. Presumably, each through hole is about several hundred microns deep, considering the thickness of the protection layer. This increases the ratio of the length of the through holes to the diameter of the same (aspect ratio), making it difficult to fabricate the print head.
Japanese Patent Laid-Open Publication No. 8-79447 proposes an optical device including a first lens array facing a document, a second lens array facing the first lens array, and one or more shield films intervening between the first and second lens arrays. The shield films are formed with apertures for passing light emitted from the first lens array. This kind of structure makes it needless to arrange mirror tubes between the lense portions or input apertures of the first lens array and the lense portions or output apertures of the second lens array.
However, the above Laid-Open Publication No. 8-79447 does not clearly show the numbers or the positions of the shield films or the positions of the apertures. Specifically, this document teaches that a single shield film is positioned substantially at the intermediate between the first and second lens arrays (see claim 3). Also, the document teaches that the apertures formed in the film each have a width capable of substantially shielding optical paths extending from the individual lens of the first lens array to the lenses of the second lens array adjoining an expected lens (see claims 4 and 9). Further, the document teaches that a first and a second shield film are provided, and that the distance between the first film and the second lens array, the distance between the second film and the first lens array and the distance between the first and second films are substantially the same (see claim 8). However, the document does not clearly teach the indices of such configurations.